Determination of Apnea type

ABSTRACT

A method of differentiating between OSA and CSA comprising: determining if chest motion above a chest motion threshold is present; determining if tracheal breath sound above a breath sounds threshold are present, classifying a state as OSA if the chest motion is above the threshold and the sounds are below the threshold; and classifying a state as CSA if both the chest motion and sounds are below their respective thresholds.

RELATED APPLICATIONS

The present application is a US national application of PCT/IL99/00188,filed Mar. 30, 1999.

FIELD OF THE INVENTION

The present invention relates to the field of determination of breathingdisorders and more particularly to the determination of Apnea andHypopnea and in particular of the type of Apnea.

BACKGROUND OF THE INVENTION

Apnea is defined as cessation of breathing activity for a certainduration (6-20 seconds). Hypopnea is either slow breathing or shallowbreathing or both. Detection of apnea/hypopnea (AH) is important in thediagnosis of the sleep apnea syndrome (SAS), a condition that afflicts2% of adult females and 4% of adult male population in westerncountries. Detection of AH is also important in the diagnosis ofbreathing irregularity conditions in children and elderly patients. Thediagnosis of SAS is traditionally performed in a sleep lab, but inrecent years devices for home analysis of performance have beendeveloped to offset the substantial cost and inconvenience of a fullsleep lab study.

Detection of AH in a sleeping subject requires identification of actualair flow into and out of the thorax. Thus, mere monitoring of chestmotion as performed with impedance pneumography is not sufficient. Theexisting technology is based on the use of thermal sensors in thenostrils and/or the use of chest and abdomen volume monitors (forexample, inductive plethysmography which is available under the tradename Respitrace™. These methods either require instrumentation of thepatient's face or use of circumferential belts around the chest andabdomen. Both approaches impose substantial inconvenience and are proneto data corruption.

One aspect of apnea detection is the prevention of sudden infant deathsyndrome (SIDS), the leading cause of death in infants 1-12 months oldin western societies. While the etiology of SIDS is obscure, it isbroadly believed that if the cessation of breathing is detected in timeand resuscitate measures are taken the baby can be saved. Based on thisnotion many monitoring devices for home use have been introduced intothe market. Unfortunately, the technology of many such devices resultsin many false alarms being activated, often wearing the mental stabilityof the parents to the point where use of the device is discontinued.

Most of the existing devices rely on monitoring the electrical impedanceof the chest However, the chest impedance shows continued substantialoscillations when the breath is held due to the action of the heartwithin the chest. To prevent this cardiac activity from being detectedas breathing activity, the detection algorithm parameters and thresholdmust be set such that false detection of apnea is almost inevitable. Inpractice, chest impedance measurements appear to be incapable ofproviding a clear indication of apnea without at the same time causingan undesirably high number of false alarms.

In PCT application PCT/IL97/00318, filed Sep. 30, 1997 and published asWO 98/144116 on Apr. 9, 1998, the disclosure of which is incorporatedherein by reference, the present inventor described a breath soundsanalysis system which includes a methodology for the detection of breathsounds in which at least one breath related sensor is placed around therespiratory system of a patient for measuring breath sound data signals;a breath analyzer which continuously matches the breath sound datasignals produced by the at least one breath related sensor to at least aregular breath sound template to determine the presence of breathing andwhich provides an alert indication when no breathing is present for atime period longer than a given period.

In addition, the PCT application describes a method of determining thestate of breathing of a patient, the method comprising determining theinspiration/expiration phase of a breath from chest movement data anddefining a breath phase variable therefrom; if the tracheal breath sounddata are significant and if the external noise is low determining if thetracheal breath sound data has a generally normal shape; and if notdetermining if the lack of flow indicates the presence of apnea and, ifso, setting an apnea alarm. Preferably, the method includes generating aloud noise indication if the breath shape is not normal.

In a preferred embodiment of the invention described in the PCTapplication, the amplitude of the level of breath sounds are comparedwith an adaptive breath sounds threshold during consecutive periods oftime. If the sound level is below a given level or if the detected sounddoes not match the spectral characteristic of authentic tracheal breathsounds, for a number of consecutive time periods an alarm may besounded.

In preferred embodiments of the invention described in the PCTapplication, the breath sounds are identified as authentic breath soundsby matching the spectrum of the sounds to a spectrum which is determinedduring a reference period and/or by determining whether the spectralshape of the sounds, as characterized by certain parameters, is normal.

SUMMARY OF THE INVENTION

One aspect of the present invention presents an improved method andapparatus for the determination of apnea and hypopnea.

In a preferred embodiment of a method of the present invention, spectralpower is used to determine the presence or absence of breath sounds. Ina preferred embodiment of the invention, the average or integral of thesound power amplitude over a particular frequency range is used as ameasure of the total breath flow. If the measure is below a threshold,an hypopnea alarm is preferably activated. If the measure is below asecond, lower value, an apnea alarm is preferably activated.

In accordance with a further aspect of the invention, a running timeaverage of the spectral power is used in the determination of apneaand/or hypopnea. The averaging time is made relatively short when it isdesired to test for apnea in SIDS and relatively longer when sleeptesting of adults is performed.

A third aspect of the invention is related to the measurement of breathsounds in the presence of noise. In the above referenced PCTapplication, an ambient sound sensor was used in order to determine thelevel of ambient sound. If the level of sound was too high, then nomeasurements were taken. In critical testing, such as SIDS testing, itis important to continue the testing even in the presence of some noise,as might be present in a household, such as a television in an adjoiningroom or the like.

In a preferred embodiment of the invention, the ambient sound is treatedin the same manner as the breath sound. For frequencies at which theambient sound level is higher than a certain level, the breath soundspectrum at that frequency is ignored in determining the breath soundpower and flow. If the power of the ambient sound is above the certainlevel for too great a portion of the relevant spectrum, the measurementof breath power is aborted and an ambient noise indication is activated.

A fourth aspect of the invention involves the differentiation betweenObstructive Sleep Apnea (OSA) and Central Sleep Apnea (CSA). While boththese conditions involve cessation of breathing, with potentially lethalimplications, the treatment for the two conditions is different. Inparticular, OSA is generally treated surgically or by a pressure devicethat overcomes the obstruction and CSA is not helped by either of thesetherapies and generally requires a neurological evaluation to determinetreatment.

In accordance with a preferred embodiment of the invention, the twoconditions are differentiated by determining if there is chest motion(expansion and contraction). When there is expansion and contraction ofthe chest, but no tracheal breath sounds, this absence of sound ispresumed to be caused by an obstruction and the Apnea is classified asof the OSA type. If there are neither breathing movements nor sound,then the apnea is presumed to be centrally caused and the apnea ispresumed to be of the CSA type.

There is thus provided, in accordance with a preferred embodiment of theinvention a method of differentiating between OSA and CSA comprising:

determining if chest motion above a chest motion threshold is present;

determining if tracheal breath sound above a breath sounds threshold arepresent;

classifying a state as OSA if the chest motion is above the thresholdand the sounds are below the threshold; and

classifying a state as CSA if both the chest motion and sounds are belowtheir respective thresholds.

Preferably, determining is performed on time segments of the chestmotion and breath sounds.

Preferably, the chest motion threshold is determined based on apercentage of motion during normal breathing. Preferably, the chestmotion threshold is between about 5% and about 10%. Preferably, thechest motion threshold is about 10% of a normal breathing chest motion.

In a preferred embodiment of the invention, the normal breathing isnormal breathing during sleep.

In a preferred embodiment of the invention, determining whether trachealbreath sounds are present includes:

producing a spectrum of the breath sound signal;

summing averaging the spectrum over a given frequency range to produce abreath sounds power signal.

Preferably, the method includes producing a separate breath soundspectrum for each of a plurality of given time periods.

In a preferred embodiment of the invention, the method includes:

producing a breath sounds power signal representative of the breathsounds power in a plurality of given time periods; and

integration circuitry which receives the breath sounds power signal; and

producing a running time average or integral of the breath sounds powersignal over a second given time period.

There is further provided, in accordance with a preferred embodiment ofthe invention, breath sounds apparatus for classifying a breathing statecomprising:

a chest motion sensor and produces a chest motion signal;

a tracheal breath sound sensor that produces a breath sound signal;

computing circuitry that receives the breath sound signal and the chestmotion signal and determines if chest motion above a chest motionthreshold is present and if tracheal breath sound above a breath soundsthreshold is present and classifies a breathing state as OSA if thechest motion is above the threshold and the sounds are below thethreshold and classifies a breathing state as CSA if both the chestmotion and sounds are below their respective thresholds.

In a preferred embodiment of the invention, the computing circuitryincludes:

spectrum producing circuitry which receives the breath sound signal andproduces a spectrum of the breath sound signal; and

averaging circuitry which receives the spectrum and sums or averages thespectrum over a given frequency range to produce a breath sounds powersignal, wherein the breath sounds power signal is used in thedetermination of whether the breath sounds are above their threshold.

There is further provided, in accordance with a preferred embodiment ofthe invention, apparatus for the detection of breathing activity,comprising:

a breath sound sensor which produces a breath sound signal responsive tobreath sounds of a subject;

spectrum producing circuitry which receives the breath sound signal andproduces a spectrum of the breath sound signal;

averaging circuitry which receives the spectrum and sums or averages thespectrum over a given frequency range to produce a breath sounds powersignal.

In preferred embodiments of the invention the given frequency range hasa lower frequency limit of at least 200 Hz, 250 Hz, 300 Hz or 400 Hz. Inpreferred embodiments of the invention the given frequency range has anupper frequency limit of 1200 Hz or less, 1300 Hz or less, 1400 Hz orless, 1500 Hz or less, 1800 Hz or less or 2000 Hz or less.

In a preferred embodiment of the invention the spectrum producingcircuitry produces a separate breath sound spectrum for each of aplurality of given time periods.

There is further provided, in accordance with a preferred embodiment ofthe invention, apparatus for the classification of breathing activity,comprising:

a breath sensor which produces a breath sound signal responsive tobreath sounds of a subject;

breath sounds power circuitry which receives the breath sounds signaland produces a breath sounds power signal representative of the breathsounds power in a plurality of given time periods; and

integration circuitry which receives the breath sounds power signal andproduces a running time average or integral of the breath sounds powersignal over a second given time period.

Preferably, the breath sounds power circuitry comprises:

spectrum producing circuitry which receives the breath sound signal andproduces a spectrum of the breath sound signal; and

averaging circuitry which receives the spectrum and sums or averages thespectrum over a given frequency range to produce the breath sounds powersignal.

In preferred embodiments of the invention the given time period isgreater than 20, 50 or 75 msec. In preferred embodiments of theinvention, the given time period is shorter than 200, 150, 100, 75 or 50msec.

In accordance with a preferred embodiment of the invention, theapparatus includes integration circuitry which receives the breathsounds power signal and produces a running time average or integral ofthe breath sounds power signal over a second given time period.

In preferred embodiments of the invention the second given time periodis at least 5 seconds, about 6 seconds, about 8 seconds, about 10seconds, between about 10-15 seconds or between about 15-20 seconds.

Preferably, the apparatus includes comparison circuitry which receivesthe averaged or integrated breath sounds power signal and produces anapnea indication if the averaged breath sounds power signal is below agiven apnea threshold. Preferably the given apnea threshold is based ona breath sounds power signal acquired during normal breathing.Preferably, the given apnea threshold is about 10% of the a breathsounds power signal acquired during normal breathing. Preferably, thegiven apnea threshold is between 5% and 10% of the a breath sounds powersignal acquired during normal breathing.

Preferably the apparatus includes comparison circuitry which receivesthe averaged or integrated breath sounds power signal and produces anhypopnea indication if the averaged breath sounds power signal is belowa given hypopnea threshold. Preferably, the given hypopnea threshold isbased on a breath sounds power signal acquired during normal breathing.Preferably the given hypopnea threshold is about 25% of the a breathsounds power signal acquired during normal breathing. Preferably, thegiven apnea threshold is between 20% and 30% of the a breath soundspower signal acquired during, normal breathing.

In a preferred embodiment of the invention, the apparatus includes:

an ambient sound sensor which produces an ambient sound signalresponsive to ambient sounds;

spectrum producing circuitry which receives the ambient sound signal andproduces a spectrum of the ambient sound signal;

comparison circuitry which compares the spectrum of the ambient soundspectrum with a threshold spectrum and produces a signal for thosefrequencies for which the spectrum is greater than the threshold; and

spectrum conditioning circuitry which conditions the breath soundspectrum by replacing the value of the breaths sounds spectrum by adifferent value for those frequencies for which the ambient soundspectrum exceeds the threshold.

There is further provided, in accordance with a preferred embodiment ofthe invention, apparatus for conditioning a breath sound signal toreduce the effects of ambient sound, comprising:

a breath sound sensor which produces a breath sound signal responsive tobreath sounds of a subject;

spectrum producing circuitry which receives the breath sound signal andproduces a spectrum of the breath sound signal;

an ambient sound sensor which produces an ambient sound signalresponsive to ambient sounds;

spectrum producing circuitry which receives the ambient sound signal andproduces a spectrum of the ambient sound signal;

comparison circuitry which compares the spectrum of the ambient soundspectrum with a threshold spectrum and produces a signal for thosefrequencies for which the spectrum is greater than the threshold; and

spectrum conditioning circuitry which conditions the breath soundspectrum by replacing the value of the breaths sounds spectrum by adifferent value for those frequencies for which the ambient soundspectrum exceeds the threshold.

Preferably the threshold is based on an ambient sounds spectrum producedin the absence of substantial ambient sound. Preferably, the thresholdat a given frequency is determined, from a plurality of spectra of theambient sound, as the average of value of the spectrum at the givenfrequency plus a factor times the standard deviation of the values ofthe spectrum. Preferably, the factor is more than 3 or between 4 and 6.

In a preferred embodiment of the invention the spectrum conditioningcircuit replaces the value of the breaths sounds spectrum by a zero forthose frequencies for which the ambient sound spectrum exceeds thethreshold. Alternatively, the spectrum conditioning circuit replaces thevalue of the breaths sounds spectrum by a value equal to the average ofvalues for adjacent frequencies, for those frequencies for which theambient sound spectrum exceeds the threshold.

There is further provided, in accordance with a preferred embodiment ofthe invention, a method differentiating between OSA and CSA comprising:

determining if chest motion above a chest motion threshold is present;

determining if tracheal breath sound above a breath sounds threshold arepresent;

classifying a state as OSA if the chest motion is above the thresholdand the sounds are below the threshold; and

classifying a state as CSA if both the chest motion and sounds are belowtheir respective thresholds.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood form the following descriptionof preferred embodiments thereof read in conjunction with the attacheddrawings in which:

FIG. 1A is a simplified block diagram of a method of determining thepresence of apnea and/or hypopnea, in accordance with a preferredembodiment of the invention;

FIG. 1B is a simplified block diagram of a method of differentiatingbetween OSA and CSA, in accordance with a preferred embodiment of theinvention; and

FIG. 2 is a cross-sectional drawing of a breath sounds sensor inaccordance with a preferred embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Reference is made to FIG. 1A which is a block diagram of a method ofdetermining the presence of apnea and/or hypopnea, in accordance with apreferred embodiment of the invention.

A tracheal breath sound sensor, placed for example on the anterior neck,over the sternal notch and/or over the anterior chest picks up atracheal sound signal (at 100). This signal is preferably amplified andfiltered (at 102). It has been found that a suitable filter is a 75-4000Hz band pass filter, although other ranges may be used. The filteredsignal is digitized using an A/D converter (at 104). It has been foundthat a 12 bit A/D is suitable, however, an A/D having a resolutionbetween 8 bits and 16 bits may also be used. It has been found that asampling rate of 8,000-15,000 samples/second, most preferably 11,025samples/second, is suitable for the present invention. However, the ahigher or lower rate is also suitable. The digitized signal is timesegmented into time segments having a period of between preferably20-100 msec, with about 50 msec being preferred (at 105) prior tofurther processing which is performed separately on each time segment. Adigital FFT transformation is applied to each segment of the digitizedsignal (at 106) and a portion (or portions) of the resulting spectrum isselected (at spectrum portion selector 108) for measuring the power.

In a preferred embodiment of the invention, the spectrum portionselector selects the portion of the spectrum between about 200-1200 Hz.This effectively removes cardiac sounds from the signal and leaves thosefrequencies which are most characteristic of breath sounds. Forchildren, a higher low frequency boundary is preferably used (forexample, 250 Hz), since the cardiac sounds have higher frequencies inchildren. In other preferred embodiments of the invention selectionhaving an upper frequency of 1300, 1400, 1500, 1800 or 2000 Hz may beused. The lower frequency should be sufficiently high to block outcardiac sounds. Thus in addition to the preferred low end of the rangeof selection frequencies of 200 and 250 Hz, low boundary frequencies of300, 350, 400 or even higher may be used in some preferred embodimentsof the invention.

It should be noted that while, in preferred embodiments of theinvention, only the initial band pass filtering is carried out on theanalog signal and the remaining processing is carried out digitally.However, it is possible to perform all of the processing on a digitizedsignal (with a higher sampling rate to avoid aliasing) or to performmore of the processing on the analog signal.

An ambient sounds sensor detects ambient sounds and a resulting signalis subjected to the same processing as the breath sounds signal (at 110,112, 114, 115, 116 and 118). Each element of the resulting ambientspectrum is compared to a threshold spectrum (at 120) and if thespectrum at any frequency is greater than the threshold, the breathsound spectrum value is set to zero for that frequency or frequencies(at 122). Alternatively, a value equal to the average of the adjacenttwo or four frequencies is substituted for the value at that frequency.Preferably, if an excessive proportion of the ambient sound spectrum isabove the threshold, an indication of excess ambient sound (at 121),such as an alarm, results. It will be noted that digital filter 118 isoptional, since the resulting processing of the breath sounds spectrumis operative only for the frequencies in the band.

The conditioned breath spectrum is now preferably summed (at 124) togive the integrated energy of the breath sounds spectrum in thefrequency range of 200-1200 Hz. More preferably this integrated energyis divided by the number of frequencies utilized in the summation toreduce the effect of spectrum lines which are blanked due to a highthreshold of ambient sound at that frequency.

The sum or average (result of 124) which is a single numbercharacteristic of the sound level of the breath sounds at the time ofthe segment is then averaged over time to give a value of the totalaverage breathing activity (at 126). This running average may be anaverage over a period of between 5-20 seconds, depending on what isbeing monitored, with shorter times being used for neo-natal apnea(SIDS) and the longer times being used for a more general diagnosticsurvey of apnea and hypopnea in adults. If the time averaged signalfalls below a first threshold a determination of hypopnea is made; if itfalls below a second, lower, threshold, an indication of apnea is made(at 130).

In the determination of apnea and hypopnea described above, thresholdvalues are utilized for measurements of the spectral lines of theambient sound and for the determination of apnea and hypopnea. Thesethresholds are found in the following manner.

During a rest period in which ambient noise is suppressed (ornon-existent) 110-118 are carried out over a period of several seconds.The 100 or so spectra which are the result of 118 over the period areaveraged and a value equal to the average plus several times (four orfive appears to work well) the standard deviation of the values for eachof the spectral frequencies is used for the threshold of 120 for thatfrequency. Similarly, during this period, steps 108-126 are carried outto give a baseline value of breath sound strength. In a preferredembodiment of the invention, the threshold of 128 is set at 25% of thisbaseline for hypopnea and 10% of the baseline for apnea. It should beunderstood that these numbers are somewhat arbitrary, but are goodpractical values which correspond to results of conventional sleep labstudies.

In a further preferred embodiment of the invention, discrimination ismade between Obstructive Sleep Apnea (OSA) and Central Sleep Apnea(CSA). In accordance with a preferred embodiment of the invention, thetwo conditions are differentiated by determining if there is chestmotion (expansion and contraction). When there is expansion andcontraction of the chest, but no tracheal breath sounds, this absence ofsound is presumed to be caused by an obstruction and the Apnea isclassified as of the OSA type. If there are neither breathing movementsnor sound, then the apnea is presumed to be centrally caused and theapnea is presumed to be of the CSA type.

This is illustrated with the help of FIG. 1B in which an output of achest motion detector of any suitable type, such as a belt type or othertype, known in the art, are used. This output is segmented in time so asto provide an indication of breathing activity.

A threshold is determined for chest motion. In a preferred embodiment ofthe invention, the chest motion is averaged over a period of normalbreathing, preferably, during sleep. The apnea chest motion threshold isthen set at some low value of this average, typically 10%. However, aswith the breath sounds average, a lower level may be used.

If the motion is above the threshold (step 142) then, if the breathsound, determined at 128 is also above the apnea threshold for breathsound, apnea is not present. On the other hand, if the chest motion isabove the threshold and the tracheal sound is below the threshold, thisindicates an obstruction and OSA. It should be noted that chest motionof up to 30 percent of normal is not uncommon in this condition.

On the other hand if both chest motion and tracheal sound are belowtheir thresholds, then CSA is indicated.

FIGS. 1A and 1B have been presented in a mixed functional/structuralform. However, in a preferred embodiment of the invention, all of theprocessing on digital signals is carried out in a computer. As usedherein, the term circuitry means either dedicated hardware, a computerprogrammed to carry out a task or a combination of the two.

FIG. 2 shows a cross-sectional view of a breath sounds sensor inaccordance with a preferred embodiment of the invention. This breathsounds sensor is the subject of PCT application PCT/IL98/00172 titled“Sensor for Body Sounds,” the disclosure of which is incorporated hereinby reference, filed on Apr. 8, 1998 in the Israel receiving office. Thesensor of FIG. 2 includes two membranes 10 and 12 which are coupled byan intervening medium 22. Two transducers 14 and 16 are mounted on themembranes and produce signals in response to the vibrations of themembranes. When the output of transducer 16 is subtracted from that oftransducer 14 ambient sound is canceled to a substantial extent. Thisdifference signal is preferably utilized for the breath sound ofreference 100 of FIG. 1 of the present application. In addition, theoutput of transducer 16 may be used as the ambient sound sensor ofreference 110 of FIG. 1. The reader is referred to this PCT applicationfor more details of the construction and operation of the sensor.

It should be understood that while the sensor of FIG. 2 is preferred,any breath sound sensor, as known in the art may be used in the practiceof the invention, with generally separate breath sound and ambientsensors.

The present invention has been explained in the context of preferredembodiments thereof. However, many of the details which have beenpresented are part of the best mode of carrying out the invention andneed not be present in various other embodiments of the invention.Furthermore, persons of skill in the art will appreciate that willappreciate that many variations on the best mode of the invention, asthe invention is defined by the following claims are possible.

As used herein the terms “comprise”, “include” and their conjugates mean“including but not limited to”.

What is claimed is:
 1. A method of differentiating between OSA and CSAcomprising: determining if chest motion above a chest motion thresholdis present; determining if tracheal breath sound above a breath soundsthreshold are present; classifying a state as OSA if the chest motion isabove the threshold and the sounds are below the threshold; andclassifying a state as CSA if both the chest motion and sounds are belowtheir respective thresholds.
 2. A method according to claim 1 whereinsaid determining is performed on time segments of the chest motion andbreath sounds.
 3. A method according to claim 1 wherein the chest motionthreshold is determined based on a percentage of motion during normalbreathing.
 4. A method according to claim 3 wherein the chest motionthreshold is between about 5% and about 10%.
 5. A method according toclaim 3 wherein the chest motion threshold is about 10% of a normalbreathing chest motion.
 6. A method according to claim 3 wherein thenormal breathing is normal breathing during sleep.
 7. A method accordingto claim 1 wherein determining whether tracheal breath sounds arepresent includes: producing a spectrum of the breath sound signal;summing averaging the spectrum over a given frequency range to produce abreath sounds power signal.
 8. A method according to claim 7 andincluding producing a separate breath sound spectrum for each of aplurality of given time periods.
 9. A method according to claim 1 andincluding: producing a breath sounds power signal representative of thebreath sounds power in a plurality of given time periods; andintegration circuitry which receives the breath sounds power signal; andproducing a running time average or integral of the breath sounds powersignal over a second given time period.
 10. Breath sounds apparatus forclassifying a breathing state comprising: a chest motion sensor andproduces a chest motion signal; a tracheal breath sound sensor thatproduces a breath sound signal; computing circuitry that receives thebreath sound signal and the chest motion signal and determines if chestmotion above a chest motion threshold is present and if tracheal breathsound above a breath sounds threshold is present and classifies abreathing state as OSA if the chest motion is above the threshold andthe sounds are below the threshold and classifies a breathing state asCSA if both the chest motion and sounds are below their respectivethresholds.
 11. Breath sounds apparatus according to claim 10 whereinthe computing circuitry includes: spectrum producing circuitry whichreceives the breath sound signal and produces a spectrum of the breathsound signal; and averaging circuitry which receives the spectrum andsums or averages the spectrum over a given frequency range to produce abreath sounds power signal, wherein the breath sounds power signal isused in the determination of whether the breath sounds are above theirthreshold.
 12. Apparatus according to claim 11 wherein the givenfrequency range has a lower frequency limit of at least 200 Hz. 13.Apparatus according to claim 11 wherein the given frequency range has alower frequency limit of at least 250 Hz.
 14. Apparatus according toclaim 11 wherein the given frequency range has a lower frequency limitof at least 300 Hz.
 15. Apparatus according to claim 11 wherein thegiven frequency range has a lower frequency limit of at least 350 Hz.16. Apparatus according to claim 11 wherein the given frequency rangehas a lower frequency limit of at least 400 Hz.
 17. Apparatus accordingto claim 12 wherein the given frequency range has an upper frequencylimit of 1200 Hz or less.
 18. Apparatus according to claim 12 whereinthe given frequency range has an upper frequency limit of 1300 Hz orless.
 19. Apparatus according to claim 12 wherein the given frequencyrange has an upper frequency limit of 1400 Hz or less.
 20. Apparatusaccording to claim 12 wherein the given frequency range has an upperfrequency limit of 1500 Hz or less.
 21. Apparatus according to claim 12wherein the given frequency range has an upper frequency limit of 1800Hz or less.
 22. Apparatus according to claim 12 wherein the givenfrequency range has an upper frequency limit of 2000 Hz or less. 23.Apparatus according to claim 11 wherein the given frequency range is atleast 800 Hz.
 24. Apparatus according to claim 11, wherein the spectrumproducing circuitry produces a separate breath sound spectrum for eachof a plurality of given time periods.
 25. Apparatus according to claim24 wherein the given time period is greater than 20 msec.
 26. Apparatusaccording to claim 24 wherein the given time period is greater than 50msec.
 27. Apparatus according to claim 24 wherein the given time periodis greater than 75 msec.
 28. Apparatus according to claim 24 wherein thegiven time period is shorter than 200 msec.
 29. Apparatus according toclaim 24 wherein the given time period is shorter than 150 msec. 30.Apparatus according to claim 24 wherein the given time period is shorterthan 100 msec.
 31. Apparatus according to claim 24 wherein the giventime period is shorter than 75 msec.
 32. Apparatus according to claim 24wherein the given time period is shorter than 50 msec.
 33. Apparatusaccording to claim 11 and including integration circuitry which receivesthe breath sounds power signal and produces a running time average orintegral of the breath sounds power signal over a second given timeperiod.
 34. Apparatus according to claim 33 wherein the second giventime period is at least 5 seconds.
 35. Apparatus according to claim 33wherein the second given time period is about 6 seconds.
 36. Apparatusaccording to claim 33 wherein the second given time period is about 8seconds.
 37. Apparatus according to claim 33 wherein the second giventime period is about 10 seconds.
 38. Apparatus according to claim 33wherein the second given time period is between about 10-15 seconds. 39.Apparatus according to claim 33 wherein the second given time period isbetween about 15-20 seconds.
 40. Apparatus according to claim 11 andincluding comparison circuitry which receives the averaged or integratedbreath sounds power signal and produces an apnea indication if theaveraged breath sounds power signal is below a given apnea threshold.41. Apparatus according to claim 40 wherein the given apnea threshold isbased on a breath sounds power signal acquired during normal breathing.42. Apparatus according to claim 41 wherein the given apnea threshold isabout 10% of the a breath sounds power signal acquired during normalbreathing.
 43. Apparatus according to claim 42 wherein the given apneathreshold is between 5% and 10% of the a breath sounds power signalacquired during normal breathing.
 44. Apparatus according to claim 11and including comparison circuitry which receives the averaged orintegrated breath sounds power signal and produces an hypopneaindication if the averaged breath sounds power signal is below a givenhypopnea threshold.
 45. Apparatus according to claim 44 wherein thegiven hypopnea threshold is based on a breath sounds power signalacquired during normal breathing.
 46. Apparatus according to claim 45wherein the given hypopnea threshold is about 25% of the a breath soundspower signal acquired during normal breathing.
 47. Apparatus accordingto claim 45 wherein the given apnea threshold is between 20% and 30% ofthe a breath sounds power signal acquired during normal breathing. 48.Apparatus according to claim 10 and including: an ambient sound sensorwhich produces an ambient sound signal responsive to ambient sounds;spectrum producing circuitry which receives the ambient sound signal andproduces a spectrum of the ambient sound signal; comparison circuitrywhich compares the spectrum of the ambient sound spectrum with athreshold spectrum and produces a signal for those frequencies for whichthe spectrum is greater than the threshold; and spectrum conditioningcircuitry which conditions the breath sound spectrum by replacing thevalue of the breaths sounds spectrum by a different value for thosefrequencies for which the ambient sound spectrum exceeds the threshold.49. Apparatus according to claim 48 wherein the threshold is based on anambient sounds spectrum produced in the absence of substantial ambientsound.
 50. Apparatus according to claim 49 wherein the threshold at agiven frequency is determined, from a plurality of spectra of theambient sound, as the average of value of the spectrum at the givenfrequency plus a factor times the standard deviation of the values ofthe spectrum.
 51. Apparatus according to claim 50 wherein the factor ismore than
 3. 52. Apparatus according to claim 51 wherein the factor isbetween 4 and
 6. 53. Apparatus according to claim 48 wherein thespectrum conditioning circuit replaces the value of the breaths soundsspectrum by a zero for those frequencies for which the ambient soundspectrum exceeds the threshold.
 54. Apparatus according to claim 48wherein the spectrum conditioning circuit replaces the value of thebreaths sounds spectrum by a value equal to the average of values foradjacent frequencies, for those frequencies for which the ambient soundspectrum exceeds the threshold.